DTC P0171: System Too Lean (Bank 1); DTC P0172: System Too Rich (Bank 1); DTC P0174: System Too Lean (Bank 2); DTC P0175: System Too Rich (Bank 2): Procedure

1. Connect the Techstream to the DLC3.
2. Turn the ignition switch to ON and turn the Techstream on.
3. Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.
4. Read DTCs.
   RESULT
   
   

   Result	Proceed to
   P0171, P0172, P0174 or P0175 is output	A
   P0171, P0172, P0174 or P0175 and other DTCs are output	B

   HINT: 

   If any DTCs other than P0171, P0172, P0174 or P0175 are output, troubleshoot those DTCs first.

B → See step   20 

A: Go to next step 

1. Check the PCV hose connections.

   OK

   PCV hose is connected correctly and is not damaged.

NG → REPAIR OR REPLACE PCV HOSE 

OK: Go to next step 

1. Check the air induction system for vacuum leaks.

   OK

   No leaks from air induction system.

NG → REPAIR OR REPLACE AIR INDUCTION SYSTEM 

OK: Go to next step 

1. Connect the Techstream to the DLC3.
2. Start the engine and turn the Techstream on.
3. Warm up the engine at an engine speed of 2500 RPM for approximately 90 seconds.
4. Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F sensor.
5. Perform the Control the Injection Volume for A/F Sensor operation with the engine in an idling condition (press the RIGHT or LEFT button to change the fuel injection volume).
6. Monitor the voltage outputs of the A/F and HO2 sensors (AFS Voltage B1S1 and O2S B1S2 or AFS Voltage B2S1 and O2S B2S2) displayed on the Techstream.

   HINT: 

   • The Control the Injection Volume for A/F Sensor operation lowers the fuel injection volume by 12.5% or increases the injection volume by 25%.
   • Each sensor reacts in accordance with increases and decreases in the fuel injection volume.
   • The A/F sensor has an output delay of a few seconds and the heated oxygen sensor has a maximum output delay of approximately 20 seconds.

   Standard Voltage

   Tester Display (Sensor)	Injection Volumes	Status	Voltages
   AFS Voltage B1S1 or AFS Voltage B2S1 (A/F)	+25%	Rich	Less than 3.1
   	-12.5%	Lean	More than 3.4
   O2S B1S2 or O2S B2S2 (HO2)	+25%	Rich	More than 0.55
   	-12.5%	Lean	Less than 0.4

   RESULT
   
   

   Status AFS Voltage B1S1 or AFS Voltage B2S1	Status O2S B1S2 or O2S B2S2	A/F Condition and A/F Sensor Condition	Misfires	Suspected Trouble Areas	Proceed to
   Lean/Rich	Lean/Rich	Normal	-	-	A
   Lean	Lean	Actual air-fuel ratio lean	May occur	PCV valve and hose PCV hose connections Injector blockage Gas leak from exhaust system Air induction system Fuel pressure Mass Air Flow (MAF) meter Engine Coolant Temperature (ECT) sensor	A
   Rich	Rich	Actual air-fuel ratio rich	-	Injector leakage or blockage Gas leak from exhaust system Ignition system Fuel pressure MAF meter ECT sensor	A
   Lean	Lean/Rich	A/F sensor malfunction	-	A/F sensor	B
   Rich	Lean/Rich	A/F sensor malfunction	-	A/F sensor	B

   Lean: During Control the Injection Volume for A/F Sensor, the A/F sensor output voltage (AFS) is consistently more than 3.4 V, and the HO2 sensor output voltage (O2S) is consistently less than 0.4 V.

   Rich: During Control the Injection Volume for A/F Sensor, the AFS is consistently less than 3.1 V, and the O2S is consistently more than 0.55 V.

   Lean/Rich: During Control the Injection Volume for A/F Sensor of the Active Test, the output voltage of the heated oxygen sensor alternates correctly.

B → See step   11 

A: Go to next step 

1. Connect the Techstream to the DLC3.
2. Turn the ignition switch to ON and turn the Techstream on.
3. Enter the following menus: Powertrain / Engine and ECT / Data List / All Data / Coolant Temp.
4. Read the Coolant Temp twice, when the engine is both cold and warmed up.

   Standard

   With cold engine 

   Same as ambient air temperature.

   With warm engine 

   Between 80 °C and 100 °C (176 °F and 212 °F).

NG → See step   21 

OK: Go to next step 

1. Read the values using the Techstream (MAF).
   NOTE:

   • Turn the ignition switch to off.
   • Perform the inspection with the vehicle indoors and on a level surface.
   • Perform the inspection of the mass air flow meter while it is installed in the air cleaner case (installed on the vehicle).
   • During the test, do not use the exhaust air duct to perform suction on the exhaust pipe.
2. Connect the Techstream to the DLC3.
3. Turn the ignition switch to ON (do not start the engine).
4. Turn the Techstream on.
5. Enter the following menus: Powertrain / Engine and ECT / Data List / MAF.
6. Wait for 30 seconds, and read the values on the Techstream.

   Standard

   0.87 gm/sec. or less

NG → See step   22 

OK: Go to next step 

1. Check the fuel pressure. Refer to ON-VEHICLE INSPECTION - Step 2 .

NG → REPAIR OR REPLACE FUEL SYSTEM 

OK: Go to next step 

1. Check for exhaust gas leaks.

   OK

   No gas leaks.

NG → REPAIR OR REPLACE EXHAUST GAS LEAK POINT 

OK: Go to next step 

1. Disconnect the fuel injector connectors to prevent the engine from starting.
   WARNING:

   Always disconnect all of the fuel injector connectors.

   NOTE:

   Do not crank the engine for more than 2 seconds.

2. Remove the ignition coil from the cylinder head.
3. Install the spark plug onto the ignition coil.
4. Attach the spark plug assembly to the cylinder head.
5. Crank the engine for less than 2 seconds and check the spark.

   OK

   Sparks jump across electrode gap.

NG → REPAIR OR REPLACE IGNITION SYSTEM 

OK: Go to next step 

1. Check the fuel injector. Refer to INSPECTION .

NG → See step   23 

OK → See step   15 

Fig 1: Identifying Air Fuel Ratio Sensor Connector Terminal

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

1. Disconnect the A/F sensor connector.
2. Measure the resistance according to the value(s) in the table below.

   Standard Resistance (Bank 1 Sensor 1)

   Tester Connection	Condition	Specified Condition
   1 (HA1A) - 2 (+B)	20 °C (68 °F)	1.8 to 3.4 Ω
   1 (HA1A) - 4 (A1A-)	Always	10 kΩ or higher

   STANDARD RESISTANCE (BANK 2 SENSOR 1)
   
   

   Tester Connection	Condition	Specified Condition
   1 (HA2A) - 2 (+B)	20 °C (68 °F)	1.8 to 3.4 Ω
   1 (HA2A) - 4 (A2A-)	Always	10 kΩ or higher

   TEXT IN ILLUSTRATION
   
   

   *1	Component without harness connected (A/F Sensor)
   *2	Bank 1
   *3	Bank 2

NG → See step   24 

OK: Go to next step 

Fig 2: Identifying Air Fuel Ratio Sensor +B Connector

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

1. Disconnect the A/F sensor connector.
2. Turn the ignition switch to ON.
3. Measure the voltage according to the value(s) in the table below.

   Standard Voltage

   Tester Connection	Switch Condition	Specified Condition
   B33-2 (+B) - Body ground	Ignition switch ON	11 to 14 V
   B31-2 (+B) - Body ground	Ignition switch ON	11 to 14 V

   TEXT IN ILLUSTRATION
   
   

   *1	Front view of wire harness connector (to A/F Sensor)
   *2	Bank 1
   *3	Bank 2

NG → See step   18 

OK: Go to next step 

1. Disconnect the A/F sensor connector.
2. Disconnect the ECM connector.
3. Measure the resistance according to the value(s) in the table below.

   Standard Resistance (Check for Open)

   Tester Connection	Condition	Specified Condition
   B33-1 (HA1A) - B50-17 (HA1A)	Always	Below 1 Ω
   B33-3 (A1A+) - B49-1 (A1A+)	Always	Below 1 Ω
   B33-4 (A1A-) - B49-2 (A1A-)	Always	Below 1 Ω
   B31-1 (HA2A) - B50-19 (HA2A)	Always	Below 1 Ω
   B31-3 (A2A+) - B49-7 (A2A+)	Always	Below 1 Ω
   B31-4 (A2A-) - B49-8 (A2A-)	Always	Below 1 Ω

   Standard Resistance (Check for Short)

   Tester Connection	Condition	Specified Condition
   B33-1 (HA1A) or B50-17 (HA1A) - Body ground	Always	10 kΩ or higher
   B33-3 (A1A+) or B49-1 (A1A+) - Body ground	Always	10 kΩ or higher
   B33-4 (A1A-) or B49-2 (A1A-) - Body ground	Always	10 kΩ or higher
   B31-1 (HA2A) or B50-19 (HA2A) - Body ground	Always	10 kΩ or higher
   B31-3 (A2A+) or B49-7 (A2A+) - Body ground	Always	10 kΩ or higher
   B31-4 (A2A-) or B49-8 (A2A-) - Body ground	Always	10 kΩ or higher

   Fig 3: Identifying A/F Sensor System Diagram (Bank 1 Sensor 1)

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

NG → REPAIR OR REPLACE HARNESS OR CONNECTOR 

OK: Go to next step 

1. Replace the A/F sensor. Refer to REMOVAL .

NEXT: Go to next step 

1. Connect the Techstream to the DLC3.
2. Turn the ignition switch to ON.
3. Turn the Techstream on.
4. Clear the DTCs. Refer to DTC CHECK / CLEAR .
5. Turn the ignition switch off and wait for at least 30 seconds.
6. Turn the ignition switch to ON and turn the Techstream on.
7. Start the engine and warm it up.
8. Drive the vehicle in accordance with the driving pattern described in the Confirmation Driving Pattern.
9. Enter the following menus: Powertrain / Engine and ECT / Utility / All Readiness.
10. Input the DTC: P0171, P0172, P0174 or P0175.
11. Check the DTC judgment result.
    RESULT
    
    

    Result	Proceed to
    ABNORMAL (DTC P0171, P0172, P0174 or P0175 is output)	A
    NORMAL (No DTC is output)	B

B → END 

A: Go to next step 

1. Replace the ECM. Refer to REMOVAL .

NEXT: Go to next step 

1. Connect the Techstream to the DLC3.
2. Turn the ignition switch to ON.
3. Turn the Techstream on.
4. Clear the DTC. Refer to DTC CHECK / CLEAR .
5. Turn the ignition switch off and wait for at least 30 seconds.
6. Turn the ignition switch to ON and turn the Techstream on.
7. Start the engine and warm it up.
8. Drive the vehicle in accordance with the driving pattern described in the Confirmation Driving Pattern.
9. Enter the following menus: Powertrain / Engine and ECT / Utility / All Readiness.
10. Input the DTC: P0171, P0172, P0174 or P0175.
11. Check the DTC judgment result.
    RESULT
    
    

    Tester Display	Description
    NORMAL	DTC judgment completed System normal
    ABNORMAL	DTC judgment completed System abnormal
    INCOMPLETE	DTC judgment not completed Perform driving pattern after confirming DTC enabling conditions
    UNKNOWN	Unable to perform DTC judgment Number of DTCs which do not fulfill DTC preconditions has reached ECU's memory limit

NEXT → END 

1. Disconnect the A/F sensor connector.
2. Remove the A/F heater relay from the engine room relay block.
3. Measure the resistance according to the value(s) in the table below.

   Standard Resistance (Check for Open)

   Tester Connection	Condition	Specified Condition
   B33-2 (+B) - 3 (A/F heater relay)	Always	Below 1 Ω
   B31-2 (+B) - 3 (A/F heater relay)	Always	Below 1 Ω
   3 (A/F heater relay) - Body ground	Always	Below 1 Ω

   Standard Resistance (Check for Short)

   Tester Connection	Condition	Specified Condition
   B33-2 (+B) or 3 (A/F heater relay) - Body ground	Always	10 kΩ or higher
   B31-2 (+B) or 3 (A/F heater relay) - Body ground	Always	10 kΩ or higher

NG → REPAIR OR REPLACE HARNESS OR CONNECTOR 

OK: Go to next step 

Fig 4: Identifying Relay Test Terminals

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

1. Remove the A/F sensor heater relay from the engine room relay block.
2. Measure the resistance according to the value(s) in the table below.

   Standard Resistance

   Tester Connection	Condition	Specified Condition
   3 - 5	Battery voltage not applied	10 kΩ or higher
   	Battery voltage applied to terminals 1 and 2	Below 1 Ω

NG → REPLACE AIR FUEL RATIO SENSOR HEATER RELAY 

OK → See step   25